U.S. patent application number 14/269820 was filed with the patent office on 2014-11-13 for electrical rotating machine.
This patent application is currently assigned to Hitachi, Ltd.. The applicant listed for this patent is Hitachi, Ltd.. Invention is credited to Motonobu IIDUKA, Makoto IMURA, Takayuki KOYAMA, Takeshi MORI, Shigeki NAKAE, Tomohiro NARUSE.
Application Number | 20140333174 14/269820 |
Document ID | / |
Family ID | 51864288 |
Filed Date | 2014-11-13 |
United States Patent
Application |
20140333174 |
Kind Code |
A1 |
IMURA; Makoto ; et
al. |
November 13, 2014 |
Electrical Rotating Machine
Abstract
An electrical rotating machine is provided with a salient-pole
rotor, which is composed of magnetic field pole bodies integrally
formed with a shaft and pole shoes constituting magnetic field pole
heads. Each pole shoe is fixedly joined on the corresponding one of
the magnetic field pole bodies with a plurality of bolts. Each pole
shoe or its corresponding magnetic field pole body is provided with
at least one protrusion or recess for restricting a
conically-shaped compression domain in a compression domain that
occurs in the pole shoe when the pole shoe is joined on the
corresponding magnetic field pole body with the bolts.
Inventors: |
IMURA; Makoto; (Tokyo,
JP) ; NARUSE; Tomohiro; (Tokyo, JP) ; IIDUKA;
Motonobu; (Tokyo, JP) ; NAKAE; Shigeki;
(Tokyo, JP) ; MORI; Takeshi; (Tokyo, JP) ;
KOYAMA; Takayuki; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi, Ltd. |
Tokyo |
|
JP |
|
|
Assignee: |
Hitachi, Ltd.
Tokyo
JP
|
Family ID: |
51864288 |
Appl. No.: |
14/269820 |
Filed: |
May 5, 2014 |
Current U.S.
Class: |
310/216.113 |
Current CPC
Class: |
H02K 1/24 20130101 |
Class at
Publication: |
310/216.113 |
International
Class: |
H02K 1/28 20060101
H02K001/28; H02K 1/24 20060101 H02K001/24 |
Foreign Application Data
Date |
Code |
Application Number |
May 10, 2013 |
JP |
2013-100175 |
Claims
1. An electrical rotating machine provided with a salient-pole
rotor composed of magnetic field pole bodies integrally formed with
a shaft and pole shoes constituting magnetic field pole heads, each
pole shoe being fixedly joined on the corresponding one of the
magnetic field pole bodies with a plurality of bolts, wherein: each
pole shoe or its corresponding magnetic field pole body is provided
with at least one protrusion or recess for restricting a
conically-shaped compression domain in a compression domain that
occurs in the pole shoe when the pole shoe is joined on the
corresponding magnetic field pole body with the bolts.
2. The electrical rotating machine according to claim 1, wherein:
each pole shoe is provided, on the lower wall thereof on sides of
opposite ends in a longitudinal direction thereof, with rectangular
protrusions, respectively, which are of the same shape and size and
each define at least one through-hole for the corresponding one of
the bolts.
3. The electrical rotating machine according to claim 2, wherein:
each rectangular protrusion has, in the longitudinal direction of
the pole shoe, a dimension that allows only corresponding one of
the bolts to extend therethrough.
4. The electrical rotating machine according to claim 2, wherein:
each rectangular protrusion has, in the longitudinal direction of
the pole shoe, a dimension that allows corresponding two or more of
the bolts to extend therethrough.
5. The electrical rotating machine according to claim 4, wherein:
each rectangular protrusion is in a stepped shape of a height
dimension that decreases stepwise with an increasing distance from
the corresponding end of the pole shoe in the longitudinal
direction.
6. The electrical rotating machine according to claim 1, wherein:
the plurality of bolts are aligned in at least two parallel rows
and along a central axis of the shaft, and the recess is formed at
an intermediate part between adjacent two ones of the at least two
parallel rows of bolts.
7. The electrical rotating machine according to claim 1, wherein:
the plurality of bolts are aligned in at least one row and along a
central axis of the shaft, the recess is formed at an intermediate
part between the row of bolts and one of widthwise opposite sides
of the pole shoe.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority of Japanese Patent
Application 2013-100175 filed May 10, 2013, which is incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to an electrical rotating machine of
the revolving-field type, in which magnetic field pole heads and
magnetic field pole bodies are fixed together by bolted joints.
[0004] 2. Description of the Related Art
[0005] A synchronous machine is an electrical rotating machine that
can realize a large output compared with an induction machine. In
recent years, the inverter driving method has been developed so
that such synchronous machines can be operated at a desired
optional power factor. Especially in regard to synchronous machines
for hydroelectric power plants, oil plants, gas plants and the
like, there is hence an increasing move toward synchronous machines
of larger capacity.
[0006] Synchronous machines include two types, one being the
revolving-armature type, and the other the revolving-field type.
The revolving-field type is the type that a rotor provided with
magnetic field poles rotates relative to a stator with armature
windings wound thereon. The revolving-armature type outputs an
armature current via slip rings, and therefore, involves the
wearing of contact portions as a problem. On the other hand, the
revolving-field type is free of such a problem, and can simplify
the routing of wires. The use of the DC energization method allows
the revolving-field type to employ a direct current as its field
current so that the magnetomotive force of field windings can be
increased even at a low voltage. The revolving-field type which is
the subject of the present invention has, therefore, become
mainstream in recent years.
[0007] In FIGS. 1 and 2, one example of conventionally-known
revolving-field type rotors is shown. FIG. 1 is a perspective view
of the conventionally-known revolving-field type rotor, and FIG. 2
is a cross-sectional view of the conventionally-known
revolving-field type rotor. In the rotor 1 of this example, four
magnetic field poles are formed at equal angular intervals around a
shaft 1c. Like this rotor 1, at least two or greater even number of
magnetic field poles are formed on a revolving-field type rotor.
Rotors of a shape that as appreciated from FIG. 2, tip ends of the
respective magnetic field poles outwardly project as many as the
number of the magnetic field poles are collectively called
"salient-pole rotors".
[0008] A shaft body 1b of a square shape in cross-section is formed
on a longitudinally central part of the shaft 1c, and on the shaft
body 1b, four magnetic field pole bodies 1a that make up shanks of
the magnetic field poles are formed. On an outer wall of each
magnetic field pole body 1a, a pole shoe 2 that makes up a head of
the corresponding magnetic field pole is joined with plural bolts
3. Described specifically, for the bolts 3, a like plural number of
through-holes are formed through the pole shoe 2, and threaded hole
machining has been applied a like plural number of times to the
magnetic field pole body 1a at locations corresponding to the
through-holes to form threaded holes. By bringing the bolts 3,
which have been inserted in the through-holes, into threaded
engagement with the threaded holes, the pole shoe 2 is joined to
the magnetic field pole body 1a. Bolted joint portions of each
magnetic field pole, where the pole shoe 2 is fixed on the magnetic
field pole body 1a, are aligned in at least two parallel rows such
that the bolted joint portions are symmetrically located with
respect to a central axis of the shaft 1c. Further, a coil 4 is
arranged on and around outer periphery of each magnetic field pole
body 1a in a space between an outer wall of the shaft body 1b and
an inner wall of the pole shoe 2.
[0009] Incidentally, centrifugal forces are applied to each bolted
joint portion of the rotor 1 during rotation of the rotor 1. As
illustrated in FIG. 3, centrifugal forces F.sub.1, F.sub.2, F.sub.c
that are applied to each bolted joint portion of the rotor 1 act in
the axial direction of the bolt 3 and, because the acting points of
the centrifugal forces F.sub.1, F.sub.2, F.sub.c deviate from the
axial centerline of the bolt 3, moments M.sub.1, M.sub.2, M.sub.c
act on the bolted joint portion. Therefore, on the bolt 3, a
pulling stress occurs in the axial direction of the bolt 3, and a
bending stress also occurs by the moments M.sub.1, M.sub.2,
M.sub.c.
[0010] As shown in FIG. 1, each pole shoe 2 is joined on the
corresponding magnetic field pole body 1a with the plural bolts 3.
As illustrated in FIG. 4, on an outer side as viewed in a direction
perpendicular to an axis of rotation, in other words, on a
widthwise outer side of the bolted joint portions of the pole shoe
2, the pole shoe 2 tends to come loose upward from the magnetic
field pole body 1a under centrifugal forces, and hence, to result
in a phenomenon that the magnetic field pole body 1a and the pole
shoe 2 separate from each other at the plane of a joint
therebetween. Such a phenomenon becomes more pronounced as the
revolution speed required for the electrical rotating machine
becomes higher or the overall lengths of the magnetic field pole
bodies 1a and pole shoes 2 arranged on the rotor 1 become
longer.
[0011] When desired to provide a synchronous machine with a large
capacity, the rotor 1 may be made longer in the longitudinal
direction of the axis of rotation while keeping the same its
cross-section perpendicular to the axis of rotation instead of
enlarging the cross-section. When the ratio of the axial length to
the diameter of the rotor 1 increases, the pole shoe 2 undergoes a
greater bending deformation as the distance from its central part
increases toward its opposite ends, and therefore, greater bending
stresses occur at the bolted joint portions in opposite end
portions than at the remaining bolted joint portions.
[0012] In a salient-pole rotor, the outer wall of each magnetic
field pole is configured such that a magnetic gap becomes larger
toward opposite longitudinal ends of the magnetic field pole to
make a magnetic flux distribution closer to a sinusoidal waveform.
This configuration is effective for reducing harmonics that occur
in an induced electromotive force. The centrifugal force to be
borne per bolted joint portion, however, becomes greater at both
the end portions of the pole shoe 2 as indicated at areas
surrounded by solid lines in FIG. 6 compared with at its central
part. The pole shoe 2, therefore, undergoes a bending deformation
at both the end portions thereof such that it curls up there,
leading to a reduction in the magnetic gap to be maintained between
the rotor and the stator during operation of the synchronous
machine. The occurrence of such a phenomenon also becomes a cause
of torque pulsation by harmonics in an induced electromotive force,
and therefore, gives not a small influence to the output
efficiency.
[0013] In general, each bolted joint portion is strong against a
pulling force in the axial direction of the bolt 3 but is weak
against a force or moment deviating from the axial centerline of
the bolt 3, because a bending stress tends to concentrate at the
thread groove of the bolt 3. When the pole shoe 2 is sufficiently
higher in stiffness than the bolts 3, the centrifugal forces
F.sub.1, F.sub.2, F.sub.c and moments M.sub.1, M.sub.2, M.sub.c are
mostly borne by the pole shoe 2 until the magnetic field pole body
1a and the pole shoe 2 separate from each other at the plane of the
joint therebetween. When the revolution speed increases and the
separation takes place, however, the loading factor of each bolt 3
increases so that the bolt 3 may fracture.
[0014] To provide a revolving-field type synchronous machine with a
large capacity, the rotor 1 needs to be enlarged. However, the
enlargement of the rotor 1 leads to increases in the centrifugal
forces F.sub.1, F.sub.2, F.sub.c and centrifugal forces F.sub.1,
F.sub.2, F.sub.c, and therefore, the magnetic field pole body 1a
and the pole shoe 2 become prone to separation from each other at
the plane of the joint therebetween and the bolts are required to
bear increased centrifugal forces and moments. For providing a
revolving-field type synchronous machine with a large capacity, it
is thus important to ensure high strength reliability of bolted
joint portions in a salient-pole rotor.
[0015] As a measure to meet such a requirement, JP-A-50-155505[U]
discloses in FIG. 1 a technology that a rectangular protrusion is
formed on a lower wall of each magnetic field pole head with the
same height over the entire length of its corresponding magnetic
field pole shank and a lower wall of the protrusion is joined to an
upper wall of the magnetic field pole shank. According to this
technology, the magnetic field pole head can be provided with
improved bending stiffness, and therefore, a bending stress which
is to act on each bolt can be reduced. In addition,
JP-A-50-155505[U] also discloses in FIG. 1 a technology that each
magnetic field pole head is beveled at longitudinal opposite end
portions thereof to define inclined surfaces. According to this
technology, the magnetic field pole head can be reduced in mass at
the longitudinal opposite end portions thereof, thereby making it
possible to reduce bending stresses and bending moments that are to
act on bolts arranged at and around the longitudinal opposite end
portions.
[0016] On the other hand, JP-A-54-175503 [U] discloses in FIGS. 3
to 5 a technology that a protrusion is formed on a lower wall of
each magnetic field pole head on a periphery of bolted joint
portions. According to this technology, the protrusion is limited
only to the periphery of the bolted joint portions so that the
increase in the mass of the magnetic field pole head can be reduced
compared with the rotor described in JP-A-50-155505 [U].
SUMMARY OF THE INVENTION
[0017] However, the technology described in JP-A-50-155505 [U]
makes a lower side of each magnetic field pole head uniformly
protrude at the same height over the entire length thereof in the
longitudinal direction of an axis of rotation, and therefore, the
mass of the magnetic field pole head itself increases accordingly.
As a result, each bolted joint portion is required to bear an
increased centrifugal force in an axial direction of the bolt. To
cope with this problem, it may be contemplated, for example, to
increase the number of bolts or to make the bolts thicker. However,
these approaches make the bolted joint portions be located close to
each other and are not preferred, although it is possible to reduce
centrifugal forces to be borne at the bolted joint portions.
[0018] Described specifically, if the bolted joint portions are
located excessively close to each other, high stresses occur at
narrow portions flanked by bolted joint portions b1 and b2 in the
pole shoe 2 as illustrated in FIG. 5, thereby raising a potential
problem that such an excessively close arrangement of bolted joint
portions may lead to a reduction in the strength of the pole shoe
2. Further, the longitudinally opposite end portions of the pole
shoe 2 are formed thinner to reduce centrifugal forces as mentioned
above. Therefore, large stresses occur there to heighten the
possibility that the pole shoe 2 may break.
[0019] To solve the above-described problems, an object of the
present invention is to provide an electrical rotating machine
provided with a salient-pole rotor which can surely avoid fracture
of bolts and breakage of pole shoes under centrifugal forces even
when increased in capacity and operated at high revolution
speeds.
[0020] To achieve the above-described object, the present invention
is characterized in that in an electrical rotating machine provided
with a salient-pole rotor composed of magnetic field pole bodies
integrally formed with a shaft and pole shoes constituting magnetic
field pole heads, each pole shoe being fixedly joined on the
corresponding one of the magnetic field pole bodies with a
plurality of bolts, each pole shoe or its corresponding magnetic
field pole body is provided with at least one protrusion or recess
for restricting a conically-shaped compression domain in a
compression domain that occurs in the pole shoe when the pole shoe
is joined on the magnetic field pole body with the bolts.
[0021] According to the present invention, it is possible to avoid
an increase in the mass of whole pole shoes and also to avoid the
fracture of bolts or the breakage of the pole shoes, so that a
salient-pole rotor of higher strength and longer service life can
be realized. Moreover, bending deformations of the pole shoes can
be reduced. Therefore, a reduction effect can be expected for
torque pulsation during operation of a synchronous machine to
improve the power efficiency to not a little extent, and a
large-capacity and high-efficiency synchronous machine can be
realized.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a perspective view of a conventionally-known
salient-pole rotor.
[0023] FIG. 2 is a cross-sectional view, taken along a plane
perpendicular to an axis of rotation, of the salient-pole
rotor.
[0024] FIG. 3 is a diagram illustrating the distribution of
centrifugal forces acting on respective barycentric points in the
rotor during rotation.
[0025] FIG. 4 is a diagram schematically illustrating a deformation
in a widthwise direction of each pole shoe in the rotor of during
rotation.
[0026] FIG. 5 is a diagram schematically illustrating a deformation
in a longitudinal direction of each pole shoe in the rotor during
rotation.
[0027] FIG. 6 is a top plan view of each magnetic field pole,
without its pole shoe, in the rotor.
[0028] FIG. 7 is a cross-sectional view, taken along a plane
perpendicular to an axis of rotation, of an electrical rotating
machine of conventional configuration.
[0029] FIGS. 8A and 8B are views depicting an electrical rotating
machine according to a first example of conventional
configuration.
[0030] FIGS. 9A and 9B are views depicting an electrical rotating
machine according to a second example of conventional
configuration.
[0031] FIGS. 10A and 10B are explanatory diagrams of compression
domains formed by joining with bolts.
[0032] FIGS. 11A and 11B are partial configuration diagrams of an
electrical rotating machine of Example 1.
[0033] FIGS. 12A and 12B are partial configuration diagrams of an
electrical rotating machine of Example 2.
[0034] FIGS. 13A and 13B are partial configuration diagrams of an
electrical rotating machine of Example 3.
[0035] FIGS. 14A and 14B are partial configuration diagrams of
electrically rotating machines of Example 4.
[0036] FIGS. 15A and 15B are partial configuration diagrams of
electrically rotating machines of Example 5.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0037] A description will first be made of the configuration of an
electrical rotating machine, to which the present invention is
applicable. This electrical rotating machine is a synchronous
machine provided with a salient-pole rotor.
[0038] As depicted in FIG. 7, the electrical rotating machine, to
which the present invention is applicable, is generally constructed
of a rotor 1 on a rotating side and a stator 7 on a stationary
side. The rotor 1 is of the revolving-field type that includes a
plurality of magnetic field poles, specifically a salient-pole
rotor. A description will hereinafter be made taking, as an
example, a case in which four magnetic field poles are formed.
However, the gist of the present invention is not limited to such
an electrical rotating machine, but can be applied to all
electrical rotating machines the magnetic field poles of each of
which consist of an even number of magnetic field poles other than
4 magnetic field poles.
[0039] The rotor 1 is a salient-pole rotor with pole shoes 2, which
make up the heads of respective magnetic field poles and project on
the side of an outer periphery of the rotor 1. The magnetic field
pole bodies 1a, which make up shanks of the respective magnetic
field poles, are integrally formed on a shaft body 1b, which is in
turn formed integrally with a shaft 1c. In spaces formed by
outwardly extending widthwise opposite sides of the pole shoes 2
from the corresponding magnetic field pole bodies 1a, copper-made
coils 4 are arranged. Each coil 4 can be in the form of a block or
a stack of thin sheets. Each magnetic field pole body 1a and its
corresponding coil 4 are divided by an unillustrated thin sheet
made of an insulating material to insulate a field current, which
flows through the coil 4, from the magnetic field pole body 1a.
[0040] The pole shoes 2 are constructed such that, when seen on a
cross-section perpendicular to the axis of rotation, they have an
arcuate shape to form an outer surface of the rotor 1 and have the
same cross-section in the longitudinal direction of the axis of
rotation. The field current of a synchronous machine may be DC
electricity, which is smaller in loss than AC electricity.
Accordingly, each pole shoe 2 may have a single block structure in
the former case, or may have a structure with magnetic steel sheets
stacked in the longitudinal direction of the axis of rotation.
[0041] As illustrated in FIG. 5, each pole shoe 2 also extends
outwardly at longitudinal opposite ends thereof from the magnetic
field pole body 1a. In spaces formed between longitudinal opposite
end portions of the pole shoe 2 and the shaft body 1b, coils 4 are
arranged. To prevent the pole shoe 2 from undergoing a bending
deformation under centrifugal forces such that it curls up, the
longitudinal opposite end portions of the pole shoe 2 are beveled
to have a thinner thickness in this example. The coils 4 arranged
in the above-described spaces are shorter compared with the coils 4
arranged in parallel with the longitudinal direction of the pole
shoe 2.
[0042] The rotor 1 is assembled by joining each pole shoe 2 to its
corresponding magnetic field pole body 1a with bolts. Locations
where the pole shoe 2 is joined with the bolts (which will
hereinafter be referred to as "bolted joint portions) are arranged
in at least two rows, bilaterally symmetrically with respect to the
central axis of rotation indicated by an alternate long and short
dash line in FIG. 6. With no intention to specifically restrict the
present invention, it may be contemplated to arrange bolted joint
portions at three or more locations in each of the opposite end
portions of the pole shoe 2. As illustrated in FIG. 6, the bolted
joint portions arranged in two or more rows in parallel to the
central axis of rotation are aligned such that in each row, a line
which connects the axial centers of the respective bolts extends
straight in the direction of the x-axis. In the direction of the
y-axis in FIG. 6, on the other hand, the bolted joint portions are
similarly aligned such that they are arranged in a multiplicity of
rows perpendicular to the central axis of rotation, and in each
row, a line which connects the axial centers of the respective
bolts extends straight.
[0043] The stator 7 is fabricated by stacking a plurality of
magnetic steel sheets in the longitudinal direction of the axis of
rotation. On an inner peripheral side of the stator 7, a plurality
of teeth is formed to facilitate the winding of armature windings.
Between the stator 7 and the rotor 1, there is a clearance to
define a magnetic gap of an adequate width. The stator 7 and rotor
1 are substantially cylindrical, and are arranged opposite to each
other such that their longitudinal centerlines coincide with each
other.
[0044] To clarify the characteristic features of the electrical
rotating machine according to the present invention, a description
will first be made based on electrical rotating machines of
conventional configurations.
[0045] FIGS. 8A and 8B are views depicting an electrical rotating
machine according to a first example of conventional configuration.
FIGS. 9A and 9B are views depicting an electrical rotating machine
according to a second example of conventional configuration. A pole
shoe 2 in FIGS. 9A and 9B extends downward in the figures with the
same rectangular cross-section. In the figures, the arrow marks
indicate a direction in which the pole shoe 2 with plural
through-holes formed therethrough for bolts is pressed against the
magnetic field pole body 1a with a like plural number of threaded
holes formed therein.
[0046] FIGS. 10A and 10B are cross-sectional views of one widthwise
sides of pole shoes in each magnetic field poles of salient-pole
rotors of two types, one having pole shoes 2 not extending downward
and the other being provided with pole shoes 2 extending downward,
taken along planes perpendicular to the axes of rotation,
respectively. When a tightening force is applied to bolts 3, the
bolts 3 are brought into a pulled state. The pole shoe 2, which is
on the side to be joined, is brought into a compressed state, and
therefore, the bolts 3 and the pole shoe 2 are brought into a
dynamically balanced state. In the figures, domains where the pole
shoes 2 bear compression loads occurred by the tightening
(hereinafter referred to as "compression domains") are
indicated.
[0047] As illustrated in FIGS. 10A and 10B, the compression domains
are formed with surfaces, to which the bolts come into contact, on
the sides of the pole shoes 2, 2 serving as origins. The
compression domains first expand in conical forms (hereinafter
called "the conically-shaped compression domains 5a, 5a"). When the
conically-shaped compression domains 5a, 5a then reach a lower wall
of the pole shoe 2 and an outer wall of a protrusion 2a formed on
the pole shoe 2, respectively, the conically-shaped compression
domains 5a, 5a do not expand any further. In FIG. 10B, however, the
compression domain further expands in a cylindrical form
(hereinafter called "the cylindrically-shaped compression domain
5b"). It is to be noted that in the figures, the conically-shaped
compression domains 5a, 5a are indicated by horizontal lines while
the cylindrically-shaped compression domain 5b is indicated by
vertical lines. As apparent from a comparison of FIG. 10A and FIG.
10B, the compression domain can be enlarged when the pole shoe 2 is
extended downward at the lower side thereof.
[0048] The height at which the compression domain changes from the
conically-shaped compression domain to the cylindrically-shaped
compression domain in FIG. 10B is determined by a conical angle
.phi. and a distance from the axial center of the bolt to the outer
wall of the protrusion 2a formed on the pole shoe 2 as indicated in
the figure. It is to be noted that the conical angle .phi. is
determined from the dimensions and stiffness of the pole shoe 2. In
a threaded bolted joint used in the present invention, the maximum
value of the conical angle may reach 45.degree.. The signs d.sub.h,
d.sub.w, D.sub.Ag, D.sub.A, L.sub.k, L.sub.v and L.sub.h in FIGS.
10A and 10B represent the following dimensions: [0049] d.sub.h:
Diameter of the hole formed for the unthreaded bolt shank through
the pole shoe 2 in FIG. 10A; and diameter of the hole formed for
the unthreaded bolt shank through the pole shoe 2 and protrusion 2a
in FIG. 10B. [0050] d.sub.w: Diameter of the hole formed for the
bolt head in the pole shoe 2. [0051] D.sub.Ag: Diameter of the
conically-shaped compression domain 5a at the plane of the joint
between the pole shoe 2 and the magnetic field pole body 1a. [0052]
D.sub.A: Diameter of the conically-shaped compression domain 5a at
the height where the conically-shaped compression domain 5a reaches
the outer wall of the protrusion 2a. [0053] L.sub.k: Height of the
compression domain (=the conically-shaped compression domain 5a) in
FIG. 10A; and the height of the compression domain (=the
conically-shaped compression domain 5a+the cylindrically-shaped
compression domain 5b) in FIG. 10B. [0054] L.sub.v: Height of the
conically-shaped compression domain 5a in FIG. 10B. [0055] L.sub.h:
Height of the cylindrically-shaped compression domain 5b in FIG.
10B (L.sub.v+L.sub.h=L.sub.k).
[0056] Upon application of a centrifugal force and a moment
occurred under rotation, the loading factor of the bolt 3 is
defined as the ratio of the stiffness of the bolt 3 to the sum of
the stiffness of the bolt 3 and that of the pole shoe 2. Concerning
the centrifugal force, the bearing factor of the bolt 3 is defined
as the ratio of the pulling stiffness of the bolt 3 in the axial
direction of the bolt 3 to the sum of the stiffness of the bolt 3
and that of the pole shoe 2. As to the moment, the bearing factor
of the bolt 3 is defined as the ratio of the bending stiffness of
the bolt 3 to the sum of the stiffness of the bolt 3 and that of
the pole shoe 2.
[0057] For the reduction of the loading factor of the bolt 3, it is
effective to lengthen the bolt 3 to lower its stiffness in the
axial direction and also to increase the stiffness of the pole shoe
2. For the reduction of the moment bearing factor of the bolt 3, it
is effective to enlarge the compression domain (the
conically-shaped compression domain 5a, or the conically-shaped
compression domain 5a+the cylindrically-shaped compression domain
5b) to be formed in the pole shoe 2 such that the pole shoe 2 is
provided with greater bending stiffness. Preferably, the
conically-shaped compression domain 5a or the cylindrically-shaped
compression domain 5b may be set to have a maximum outer diameter
at the height of the plane of a joint where the pole shoe 2 and
magnetic field pole body 1a or the protrusion 2a formed on the pole
shoe 2 and the magnetic field pole body 1a are in contact to each
other. As a consequence, the pole shoe 2 is improved in second
moment of area, leading to a reduction in the bending stress that
is to occur on the bolt 3.
[0058] When the lower side of the pole shoe 2 is extended with the
same height over the entire length of the axis of rotation as
illustrated in FIG. 9A, 9B or 10B, the mass of the whole pole shoe
increases, leading to an increase in the centrifugal force to be
borne in the axial direction by the bolt 3. When the number of
bolts is increased or bolts of greater diameter are used, on the
other hand, the load to be borne by each bolt 3 is reduced.
However, the bolted joint portions come close to each other. A high
stress, therefore, occurs at narrow portions flanked by the bolted
joint portions b1 and b2 (see FIGS. 5 and 6) of the pole shoe 2,
thereby raising a potential problem that such an approach may lead
to a reduction in the strength of the pole shoe 2. Further, the
longitudinal opposite end portions of the pole shoe 2 are formed
thinner to reduce a centrifugal force, so that a larger stress
occurs at the opposite end portions than at the central part. There
is, accordingly, an increased possibility of breakage of the pole
shoe 2 at the longitudinal opposite end portions thereof.
[0059] The present invention has been made to solve the above-de
scribed problems, and embodiments of the electrical rotating
machine according to the present invention will hereinafter be
described in the following examples. It is, however, to be noted
that the following description will concentrate only on rotors as
their combined stators can be of a conventional configuration.
Example 1
[0060] FIG. 11A is a perspective view of a shaft body 1b, a
magnetic field pole body 1a, and a pole shoe 2 in a salient-pole
rotor 1 of Example 1. On the other hand, FIG. 11B is a side view of
the shaft body 1b, magnetic field pole body 1a and pole shoe 2. As
apparent from these figures, the salient-pole rotor 1 of Example 1
is characterized in that only at opposite longitudinal end portions
of the pole shoe 2, protrusions 2a are formed extending downward
with the same rectangular cross-section relative to a central part
of the pole shoe 2 to provide the pole shoe 2 with improved second
moment of area. These protrusions 2a can reduce bending stresses on
the bolts 3 in the opposite end portions of the pole shoe 2, said
bending stresses being to occur due to a deviation of a centrifugal
force, and therefore, can prevent breakage of the bolts 3.
[0061] In this example, the pole shoe 2 can be made lighter
compared with the conventional configuration. This example can,
therefore, reduce an increase in overall centrifugal force. As
illustrated in FIGS. 11A and 11B, the pole shoe 2 has a bilaterally
symmetric structure. Bolted joint portions arranged in two rows in
parallel to the axis of rotation are aligned such that in each row,
a line which connects the axial centers of the respective bolts
extends straight in the direction of the x-axis. In the direction
of the y-axis in FIG. 11A, on the other hand, the bolted joint
portions are aligned likewise. Accordingly, the pole shoe 2 has a
bilaterally symmetric structure in both a cross-section
perpendicular to the axis of rotation and a cross-section parallel
to the axis of rotation. Owing to the existence of no deviation in
mass, the pole shoe 2 itself does not undergo much bending or
twisting.
[0062] In this example, the height (L.sub.k in FIG. 10B) from a
lower wall of each protrusion 2a of the pole shoe 2 to the bearing
surface for each corresponding bolt may preferably be set equal to
the diameter of the bearing surface for the bolt or so. In this
case, the conically-shaped compression domain 5a can be maximized
by also setting the distance from the axial centerline of the bolt
to an outer wall (on the left side in FIG. 10B) of the magnetic
field pole body 1a equal to the diameter of the bearing surface for
the bolt or so.
[0063] When the distance from the axial centerline of each bolt to
the outer wall of the magnetic field pole body 1a is progressively
shortened, the magnetic field pole body 1a becomes thinner on the
side of the outer wall relative to the threaded hole (on the left
side in FIG. 10B). In this example, however, the distance from the
axial centerline of each bolt to the outer wall (on the left side
in FIG. 10B) of the magnetic field pole body 1a is also set equal
to the diameter of the bearing surface for the bolt or so, and
therefore, there is no much potential problem of a localized
reduction in the strength of the threaded hole.
[0064] Further, the dimension in the longitudinal direction of the
axis of rotation of each protrusion 2a, which extends from the pole
shoe 2--as measured from the adjacent longitudinal end of the
magnetic field pole body 1a--may be set preferably at a dimension
that the compression domain at the height of the plane of a joint
between the pole shoe 2 and the magnetic field pole body 1a has a
maximum outer diameter. However, the compression domain of the
bolted joint portion b1 on the longitudinal outermost side of the
axis of rotation and that of the bolted joint portion b2 closer by
one bolted joint portion toward the central part of the pole shoe 2
may partly overlap each other when they come close to each other
(see FIGS. 5 and 6). In such a case, the protrusion 2a may be
formed with a rectangular cross-section such that its outer shape
is located at the position of a bisector (a vertical dashed line in
FIG. 6) of a narrow portion of the pole shoe 2 between the bolted
joint portions b1 and b2. This configuration can maximize the
compression domains of the bolted joint portions b1, b2.
Example 2
[0065] FIG. 12A is a perspective view of a magnetic field pole body
1a and a pole shoe 2 in a salient-pole rotor 1 of Example 2. On the
other hand, FIG. 12B is a side view of magnetic field pole body 1a
and pole shoe 2. The salient-pole rotor of Example 2 is
characterized in that different from the salient-pole rotor of
Example 1, a wider protrusion 2a extends not only on a lower side
of the bolted joint portion b1 but also on a lower side of the
bolted joint portion b2, both, on the side of each longitudinal end
portion of the pole shoe 2 (see FIGS. 5 and 6).
[0066] It is to be noted that in the present invention, the bolted
joint portions included in each row at an area where each
protrusion 2a extends are not intended to be limited only to two
locations and each protrusion 2a may be arranged from the
corresponding longitudinal end portion of the pole shoe 2 to the
area where an n.sup.th (n: an integer of 1 or greater) bolted joint
portion is included. However, the mass of the whole pole shoe 2
increases as the protrusions 2a become longer in the longitudinal
direction of the pole shoe 2. The number of n is, therefore,
determined through a comparative consideration of the effect
available from an enlargement of the compression domains and the
extent of a deformation of the pole shoe 2 due to an increase in
its mass.
Example 3
[0067] FIG. 13A is a perspective view of a magnetic field pole body
1a and a pole shoe 2 in a salient-pole rotor 1 of Example 3. On the
other hand, FIG. 13B is a side view of magnetic field pole body 1a
and pole shoe 2. The salient-pole rotor of this example is
characterized in that the height dimensions of protrusions 2a,
which extend downward from the pole shoe 2, are lowered stepwise
from opposite longitudinal end portions of the pole shoe 2 toward a
central part of the pole shoe 2, in other words, as the distances
from the opposite longitudinal end portions of the pole shoe 2
increase. As described above, the bolted joint portions included in
each row at an area where each protrusion 2a extends downward are
not intended to be limited only to two locations in this example.
Each protrusion 2a may be arranged from the corresponding
longitudinal end portion of the pole shoe 2 to the area where an
n.sup.th (n: an integer of 1 or greater) bolted joint portion is
included, and the height dimensions of protrusions 2a, which extend
downward from the pole shoe 2, are lowered stepwise from opposite
longitudinal end portions of the pole shoe 2 toward a central part
of the pole shoe 2.
[0068] In such a case that the ratio of the length of the magnetic
field pole body 1a in the direction of the x-axis to the width of
the magnetic field pole body 1a in the direction of the y-axis is
great, the mass of the whole pole shoe 2, therefore, does not
increase compared to the conventional configuration. Further, it is
possible to stepwise adjust, in the longitudinal direction of the
axis of rotation, a bending stress that occurs on each bolt 3, and
also, such a bending deformation that would cause curling-up of the
pole shoe 2.
Example 4
[0069] FIGS. 14A and 14B are schematic diagrams of salient-pole
rotors 1, 1 of Example 4 in cross-sections perpendicular to the
axes of rotation. No rectangular protrusion is arranged on a lower
wall of a pole shoe 2 in FIG. 14A, while a rectangular protrusion
2a is arranged on a lower wall of a pole shoe 2 in FIG. 14B. The
salient-pole rotor 1 of FIG. 14A is characterized in that at the
plane of a joint between a magnetic field pole body 1a and the pole
shoe 2, a clearance of small height is formed as a recess 6 at an
intermediate part between each combination of bolted joint
portions, which are adjacent to each other in a widthwise direction
of the pole shoe 2 with respect to a longitudinal centerline of the
pole shoe 2. The recess 6 illustrated in the figure may be arranged
either on the side of the magnetic field pole body 1a or on the
side of the pole shoe 2. Preferably, however, the recess 6 may be
arranged on the side of the pole shoe 2 for a reduction in the mass
of the whole pole shoe 2. The salient-pole rotor 1 of FIG. 14B is
similar to the salient-pole rotor 1 of FIG. 14A, but is different
from the salient-pole rotor 1 of FIG. 14A in that the rectangular
protrusion 2a is arranged on the lower wall of the pole shoe 2 as
described above, and also, in that at the plane of a joint between
a magnetic field pole body 1a and the rectangular protrusion 2a, a
clearance of small height is formed as a recess 6 between each
combination of bolted joint portions, which are adjacent to each
other in a widthwise direction of the pole shoe 2 with respect to a
longitudinal centerline of the pole shoe 2.
[0070] The dimension of the recess 6 in the direction of the y-axis
in FIG. 14A or 14B may preferably be set such that the recess is
formed in a range indicated in the figure by two dashed lines
extending straight downward from inner ends, as viewed in the
direction of the y-axis, of respective bearing surfaces on the side
of the pole shoe, with which the associated bolts 3 are in contact.
If the dimension in the direction of the y-axis of the recess is
set greater than the above-mentioned preferred dimension, the
compression domain of each bolted joint portion becomes smaller,
and hence, a greater bending stress occurs on the corresponding
bolt.
Example 5
[0071] FIGS. 15A and 15B are schematic diagrams of cross-sections
of salient-pole rotors 1, 1 of Example 5 perpendicular to the
central axes of rotation. No rectangular protrusion is arranged on
a lower wall of a pole shoe 2 in FIG. 15A, while a rectangular
protrusion 2a is arranged on a lower wall of a pole shoe 2 in FIG.
15B. The salient-pole rotor 1 of FIG. 15A is characterized in that
clearances of small height are formed as recesses 6, 6 on
respective widthwise outer sides of each center of bolt axis, which
are adjacent to each other in a widthwise direction of the pole
shoe 2 with respect to a longitudinal centerline of the pole shoe
2. The dimension of each recess 6 in the direction of the y-axis in
FIG. 15A may preferably be set such that the recess 6 is formed in
a range between a dashed line extending straight downward from an
inner end, as viewed in the direction of the y-axis, of a bearing
surface on the side of the pole shoe 2, with which the associated
bolt 3 is in contact, and a proximal side wall of a magnetic field
pole body 1a. If the dimension in the direction of the y-axis of
the recess 6 is set greater than the above-mentioned preferred
dimension, the compression domain of each bolted joint portion
becomes smaller, and hence, a greater bending stress occurs on the
corresponding bolt. The salient-pole rotor 1 of FIG. 15B is similar
to the salient-pole rotor 1 of FIG. 15A, but is different from the
salient-pole rotor 1 of FIG. 15A in that the rectangular protrusion
2a is arranged on the lower wall of the pole shoe 2 as described
above, and also, clearances of small height are formed as recesses
6, 6 between each combination of bolted joint portions adjacent to
each other in a widthwise direction of the pole shoe 2.
[0072] The electrical rotating machines provided with the
salient-pole rotors of Examples 4 and 5, respectively, can each
make the contact pressure higher at the height position of the
plane of the joint between the pole shoe and the magnetic field
pole body, and therefore, can each suppress the occurrence of their
separation at the plane of the joint. Therefore, the embodiments of
Examples 4 and 5 can each be applied preferably to locations where
a pole shoe and its associated magnetic field pole body have become
prone to separation at the plane of the joint therebetween due to
the outward extension of the pole shoe from the magnetic field pole
body in both the longitudinal and widthwise directions of the pole
shoe. As a consequence, it is possible to achieve both a reduction
in a bending stress on each bolt and suppression of the separation
of a pole shoe and its associated magnetic field pole body at the
plane of a joint therebetween.
[0073] As has been described above, the present invention can avoid
an increase in the mass of whole pole shoes and also to avoid the
fracture of bolts or the breakage of the pole shoes, so that a
salient-pole rotor of higher strength and longer service life can
be realized. Moreover, it is possible to reduce such a bending
deformation that would cause curling-up of the pole shoes. A
large-capacity and high-efficiency synchronous machine can be
realized accordingly.
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